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Humans and other primates shift their attention to follow the gaze of others [gaze following (GF)]. This behavior is a foundational component of joint attention, which is severely disrupted in neurodevelopmental disorders such as autism and schizophrenia. Both cortical and subcortical pathways have been implicated in GF, but their contributions remain largely untested. While the proposed subcortical pathway hinges crucially on the amygdala, the cortical pathway is thought to require perceptual processing by a region in the posterior superior temporal sulcus (pSTS). To determine whether pSTS is necessary for typical GF behavior, we engaged rhesus macaques in a reward discrimination task confounded by leftward- and rightward-facing social distractors following saline or muscimol injections into left pSTS. We found that reversible inactivation of left pSTS with muscimol strongly suppressed GF, as assessed by reduced influence of observed gaze on target choices and saccadic reaction times. These findings demonstrate that activity in pSTS is required for normal GF by primates.